1. Field of the Invention
The present invention relates to a method and apparatus for a vapor deposition of diamond. More specifically, it relates a highly efficient method and apparatus for uniformly vapor depositing diamond, especially a diamond film having a sufficient thickness and good film quality at a high film deposition rate.
2. Description of the Related Art
Diamond is an allotropy of carbon (C), exhibits a diamond structure, has a high Mohs hardness of 10, and has a superior thermal conductivity of 2000 W/mk, compared with other materials.
Also known is a diamond-like carbon which is an allotropy of the same element, and is transparent and insulative, although amorphous, and this product also exhibits a high thermal conductivity and hardness although less than that of diamond. These factors enable use of this material in various ways.
More specifically, this material has attracted attention as a substrate material for mounting a semiconductor integrated circuit by utilizing the high thermal conductivity thereof, and as a coating for tools by utilizing the high hardness thereof. Also, diamond-like carbon is presently used as a vibrating plate for a speaker, when coated on the surface of a titanium (Ti) metal plate.
Especially, diamond has a thermal conductivity of 2000 W/mk, which corresponds to as much as 4-fold that of copper, and yet also has an excellent hardness and insulating property, and therefore, is an ideal material for a heat sink of a semiconductor element and as the material for a circuit substrate. Also, diamond has an excellent light transmitting property over a wide wavelength range, and thus is also an excellent optical material. Further, since diamond has a wide band gap of 5.45 eV and is a semiconductor with a high carrier mobility, it has attracted attention for use for high performance devices such as a high temperature transistor, high speed transistor, etc.
As the vapor phase method of synthesizing diamond or a diamond-like carbon, such methods as chemical vapor deposition (CVD method), ion plating, ionized vapor deposition, sputtering, etc., have been proposed and investigated. Among, these methods, that showing the highest probable bulk production is the CVD method. This method can be classified, in accordance with the method of excitation of a reactive gas, into the hot filament CVD method, the microwave plasma CVD method, and the electron assisted CVD method, etc.
More specifically, as the method for vapor phase synthesis of diamond with a good quality, there are known chemical vapor deposition (CVD methods) such as the hot filament method (S. Matsumoto et al., Japan, J. Appl. Phys. 21(1981)L183) , the microwave plasma CVD method (M. Kamo et al., J. Cryst. Growth. 62(1983)642), the electron assisted CVD method (A. Sawabe et al., Appl. Phys. Lett. 46(1985)146), etc.
However, according to these preparation methods, the film depositon rate of diamond is as low as several .mu.m/h or lower, and although using an inexpensive device and starting materials, the cost is higher due to a poor productivity, and therefore, practical application is not yet viable. Also, the high frequency thermal plasma CVD method (Society of Applied Physics, Spring Season Lecture, March 1987) has a drawback in that the surface is graphitized at a film thickness of 30 .mu.m or more, and thus, although a high film deposition rate of 1 .mu.m/min can be obtained, a thick film cannot be prepared. The thermal plasma generated by high frequency has a low flow speed and, therefore, the substrate must be placed in contact with the thermal plasma. Accordingly, the temperature of the substrate surface becomes higher, and thus a thick film cannot be prepared. Also, since a large volume thermal plasma formation occurs, the flow speed of the thermal plasma is low and does not allow a sufficiently high cooling speed of the water-cooled substrate, whereby a uniform diamond film cannot be obtained.
Therefore, although there are various deposition methods available, and the deposition of diamond can be realized by each of these methods, the deposition rate of a film with a good quality such that only the peak of diamond can be detected according to the Raman spectroscopic method is as slow as 1 .mu.m/h or less. Also, in the case of a diamond-like carbon, the deposition rate is as slow as about 10 .mu.m/h, which poses a problem with respect to bulk production.
Accordingly, there is a need for a development of a deposition method with a rapid film deposition rate.
As described above, various methods have been proposed and investigated as a method of deposition of a diamond film, but even in the best CVD method, the deposition rate of the diamond is 1 .mu.m/h or less, and therefore, the development a CVD method with a rapid film deposition rate has yet to be realized.